Radon is a naturally occurring, sparingly water soluble radioactive gas that results from the breakdown of uranium in soil, rock and water. Research has linked radon to causing cancer. In fact, the Surgeon General has reported that radon is the second leading cause of lung cancer in the United States. Although radon is more prevalent in certain areas of the U.S., radon can be found in all parts of the U.S. Therefore, the risks associated with exposure to radon gas are common throughout all parts of the U.S.
Radon can get into any type of building and build up to high levels of concentration. Since most people spend a majority of their time in their homes, people are at the greatest risk of radon exposure in their own homes. Given the potential health hazards presented by radon, the Environmental Protection Agency (EPA) suggests and some states even mandate that residential homes be tested for the presence of radon.
While no amount of exposure to radon gas is considered "safe" since any exposure to radon gas poses a health risk, the Surgeon General and the EPA recommend testing for radon and the reduction of radon in homes that have high levels. The recommendation advises reducing and maintaining radon levels in the home to less than 4 picocuries per liter (pCi/L). While radon usually enters a home by diffusion from the underlying soil, radon may also enter a home through the water delivered to the home. Homes serviced by well water are at the greatest risk of having radon contaminated water since the radon in public utility supplied water supplies is usually radon free by the time the water is delivered to the home. Radon in the well water is released into the air in the house when water is used for showers or other household tasks.
There are two fundamental methods to treat and remove radon from water contaminated by radon gas. The two techniques generally involve removing the radon by aeration or granular activated carbon (GAC) filtration. The GAC method involves filtering water through filter(s) containing carbon granules that absorb the radon gas as the water is passed through the filter at either the point-of-entry into the house or at the point-of-delivery. Radon attaches to the carbon and leaves the filtered water radon-free. An unavoidable and undesirable side effect of this method is that the radon deposited in the filter decays to Pb-214, a radioactive isotope of lead. The lead-laced carbon filters require constant monitoring and must eventually be disposed of as low-level radioactive waste. The disposal of low-level radioactive waste is an unwanted and cost-prohibitive proposition for most homeowners.
The aeration method involves introducing air into the water supply to increase the gas-liquid interface, thereby allowing the radon gas dissolved in the water to diffuse into the gas phase. The air/radon gas mixture is then vented from the water supply and the water is delivered for use radon-free. Most aeration systems include bubble towers or spray chambers requiring depressurization of the incoming water supply, dropping the water through air or bubbling air through the water to create a counter-flow between the air and water so that the introduced air "strips" or absorbs the radon dissolved in the water and then repressurizing the outgoing water. This type of system requires a significant initial capital investment in equipment that is cost-prohibitive for most homeowners. The recurring maintenance costs associated with this type of systems also makes it all but impractical to individual homeowners depending on well water. This type of system also requires a rather large space to accommodate the tower and associated equipment. If located in a home there exists the constant risk that the radon removed from the water may enter the home before being completely vented away.
A variation of the bubble tower type aeration system is disclosed in U.S. Pat. No. 5,104,554 issued to Dempsey Apr. 14, 1992. The Dempsey device injects compressed air inside of a well's casing below the well pump's inlet. The well casing, in effect, functions as a bubble tower similar to those in the previously described aeration systems. The Dempsey system may be adequate in some shallow wells where the overall depth of the well is relatively shallow. Most modern wells are deep 200 to 600 and the Dempsey system would require the use and delivery of highly compressed air &gt;100 psi in deep wells. Using highly compressed air in the Dempsey system will cause the water delivered for use to effervesce and appear unacceptably milky at the point of delivery. Additionally, a system under high pressure, especially a system under constant high pressure, is prone to increased maintenance and/or repair costs due to the high pressure continually placed on the system.